Stephanie is 4 times as old as Ben and is also 18 years older than Ben. How old is Stephanie?
Solution: We can use the given information to write down two equations that describe the ages of Stephanie and Ben. Let Stephanie's current age be $s$ and Ben's current age be $b$ $s = 4b$ $s = b + 18$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $s$ is to solve the second equation for $b$ and substitute that value into the first equation. Solving our second equation for $b$ , we get: $b = s - 18$ . Substituting this into our first equation, we get the equation: $s = 4$ $(s - 18)$ which combines the information about $s$ from both of our original equations. Simplifying the right side of this equation, we get: $s = 4s - 72$ Solving for $s$ , we get: $3 s = 72$ $s = 24$.